Figure 1.

One-carbon metabolism pathway. Homocysteine can be elevated in conditions of low folate, low vitamin B₆, or low vitamin B₁₂. The sulfhydryl groups on several proteins, including cystathionine β-synthase, in the one-carbon metabolism pathway are potential sites for interferences by Pb. Abbreviations: Ado, adenosine; BHMT, betaine-homocysteine S-methyltransferase; CBS, cystathionine β-synthase; DHF, dihydrofolate; DMG, dimethylglycine; Glu, glutamate; Gly, glycine; GSH, glutathione; MS, methionine synthase; MT, methyltransferase; MTHFR, methylenetetrahydrofolate reductase; SAH, S-adenosylhomocysteine; SAM, S-adenosylmethionine; THF, tetrahydrofolate; Zn, zinc. Adapted from Bistulfi et al. (2010). *Indicates putative locations for interference by Pb.